1. Field of the Invention
The invention relates to an improved pressure booster of a fuel injection system.
2. Description of the Prior Art
For the sake of better comprehension of the specification and claims, some terms will now be defined: The fuel injection system of the invention can be embodied as either stroke-controlled or pressure-controlled. Within the context of the invention, the term stroke-controlled fuel injection system is understood to mean that the opening and closing of the injection opening is effected with the aid of a displaceable nozzle needle as a result of the hydraulic cooperation of the fuel pressures in a nozzle chamber and in a control chamber. A pressure reduction inside the control chamber causes a stroke of the nozzle needle. Alternatively, the deflection of the nozzle needle can be effected by a final control element (actuator). In a pressure-controlled fuel injection system according to the invention, the nozzle needle is moved by the fuel pressure prevailing in the nozzle chamber of an injector, counter to the action of a closing force (spring), so that the injection opening is uncovered for an injection of the fuel out of the nozzle chamber into the cylinder. The pressure at which fuel emerges from the nozzle chamber into a cylinder of an internal combustion engine is called the injection pressure, while the term system pressure is understood to be the pressure at which fuel is available or kept on hand inside the fuel injection system. Fuel metering means furnishing a defined fuel quantity for injection. Leak fuel is understood to be a quantity of fuel that occurs in operation of the fuel injection system (such as reference leakage) and is not used for injection and is returned to the fuel tank. The pressure level of this leak fuel can have a standing pressure, and the fuel is then depressurized to the pressure level of the fuel tank.
In a fuel injection system in accordance with the teaching of German Patent Disclosure DE 199 39 428 A1, the entire high-pressure chamber in the injector and in the pressure booster must be depressurized upon the restoration of the piston of the pressure booster, resulting in high depressurization losses.
In a circuit in accordance with the teaching of German Patent Disclosure DE 199 10 970 A1, an additional control quantity occurs during the triggering of the pressure booster. This control quantity flows from the high-pressure line via a throttle and the differential chamber of the pressure booster into the leak fuel. This throttle should be designed with a small size, to reduce leakage losses. For easier, faster restoration of the piston of the pressure booster, conversely, a larger design is desirable, so that upon the restoration, excessive forces need not be overcome. In the installation space of the injector, it is not possible to achieve means for overcoming the forces that counteract the restoration, when the throttles are small. This slows down the restoration, which can sometimes not be completed before the next injection.